In mathematics, the Kronecker delta (named after Leopold Kronecker) is a function of two variables, usually just non-negative integers. The function is 1 if the variables are equal, and 0 otherwise:
This latter case is for convenience.
The following equations are satisfied:
Therefore, the matrix δ can be considered as an identity matrix.
Another useful representation is the following form:
This can be derived using the formula for the finite geometric series.